Since July of 1979, 553 Hancock "SGP" bioprostheses have been implanted in 436 patients; 105 patients have been followed more than four years. Follow-up data includes early and late mortality and causes, thromboembolic incidence, valve failures and modes of failures, six months postoperative hemodynamic data for atrioventricular and aortic implants, late greater than 4.5 years) hemodynamic data for mitral valve patients, and complications following valve replacement with the "SGP" bioprosthesis. Durability of the bioprosthesis implanted more than 4.5 years is marginal. Long-term follow-up reveals a 9% (10/105) valve failure rate in the atrioventricular positions at a mean of 77.8 months following implant. Late hemodynamic prosthetic stenosis has been found in 7 of 18 patients studied an average of 85 months after implantation. Aortic prosthesis has failed early, with 88 valves at risk. All other factors continue to be favorable regarding the Hancock "SGP" prosthesis.